strange behaviour of Galaxy Note 4

I bought a Note 4 with Android 6.0.1. I do not know if the phone is rooted. The seller told me that it has a problem: sometimes when you turn on the phone it starts normally, everything works, it charges normally, but sometimes it starts with a black screen with the Android robot and a message like "could not do normal reboot" and sometimes does not start at all. I have to take off the battery, wait few minutes, put the battery back, wait 5-10 minutes and then the phone opens normally again. It is a little strange.

I want to install clean Android 4.4.4 without any rooting or custom ROM. Just the original Android 4.4.4. I found the file on samsung-updates.com, but I am a little afraid of doing just a simple resoft with Odin, because I do not know what will happen next. What do you suggest?

Thank you for any help!

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